D. Ghose

Role of initial surface roughness on ion induced surface morphology

We report here the influence of initial surface roughness on the development of ion induced Si surface morphology. Surfaces of different initial roughness have been generated chemically and bombarded by 16.7keV O2+ ions at an oblique angle. It is observed that surface roughness enhances the initial perturbation, which aids to form the ion induced regular nanostructures at an ion fluence typically one to two orders of magnitude less than that are required to produce the same structures on an initially flat surface. This observation also explores the role of initial surface perturbation on the initiation of curvature dependent sputtering.

The angular distribution of sputtered silver atoms

Abstract Angular distributions of sputtered atoms have been determined for a Ag target under bombardment with 20 and 30 keV 20 Ne + , 40 Ar + , 84 Kr + and 132 Xe + ions both at normal and oblique angles of incidence. At normal ion incidence the distribution is symmet with respect to the target normal, while at oblique ion incidence the distribution is asymmetric in the plane containing the ion beam and the surface normal and symmetric in the transverse plane. Scanning electron microscopy of the sputtered surface shows the development of a high density array of cones in the bombarded area. The results are discussed from the viewpoint of sputtering from a very rough surface.

Growth and melting of silicon supported silver nanocluster films

Thin films of silver nanoclusters deposited on Si substrates are studied using scanning electron microscopy along with energy dispersive x-ray spectrometry. The nanoclusters are produced by dc magnetron sputtering followed by gas aggregation in a dense buffer gas. The film deposition is performed in a low impact energy regime with mass (size) selected clusters. These clusters were treated with rapid thermal annealing that gives an idea about the melting and evaporation mechanism of silver nanoclusters. Subsequent annealing of the grown silver film allows one to analyse the structure of the film and the character of its evolution. At room temperature, deposited clusters are distributed randomly, and annealing of the film leads to joining of clusters–monomers in non-compact clusters. At high temperatures, evaporation of clusters takes place. Parameters of the processes under consideration are estimated.

Effect of initial target surface roughness on the evolution of ripple topography induced by oxygen sputtering of Al films

The effect of pre-existing random roughness on the evolution of ripple structures in O2+ sputtered thin Al films has been investigated. The results show that there is a considerable reduction in initial roughness of the film surface at the early stages of sputtering. For large scale surface structures, angle-dependent first order sputtering is responsible for ion beam smoothening, while for smaller microscopic features, different relaxation mechanisms dominate for smoothing of the surface. At the later stages of sputtering, the curvature dependent erosion instability sets in leading to the development of either coherent ripples or faceted structures depending on the degree of virgin film roughness and bombarding angle. It is found that coating a flat Si surface with ultrathin Al film and subsequent removal of the Al layer by oblique O2+ sputtering leads to the formation of ripple pattern with moderate amplitude in the Si matrix at much lower effective fluence than that would be in bare Si without Al masking.

Microstructural and Chemical Evolution of -CH3-Incorporated (Low-k) SiCO(H) Films Prepared by Dielectric Barrier Discharge Plasma

The present work focuses on the incorporation of -CH 3 radicals in organic SiCO(H) films with low dielectric constant (k = 2.46). The SiCO(H) films were deposited by dielectric barrier discharge plasma method using a mixture of CH 4 and Ar gases at different conditions (varying the frequency and pressure). The evolution of the film microstructure was investigated by means of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) absorption spectroscopy, and atomic force microscopy (AFM). Various bonds, C-C, C-O, Si-O, and Si-CH 3 , were observed in XPS. In XPS analysis, it is observed that at higher frequency range (from 1 to 5 kHz), -CH 3 radicals (in the form of Si-CH 3 ) increase significantly. FTIR absorption spectra consist of several vibrational bands: namely, Si-O-Si asymmetric stretching at 1034 cm -1 , symmetric deformation of the -CH 3 group in Si-CH 3 configuration at 1270 cm -1 , C-H stretching of-CH x (x = 2 and 3) groups in the region between 3050 and 2750 cm -1 , and -OH related vibrational bands in the range between 3700 and 3150 cm -1 . The change in various deposition parameters causes the change in different Si-O-Si vibrational band ratio, and the intensity of C-H x and Si-CH x . The film roughness was verified by AFM measurement.

Anomalous patterns and nearly defect-free ripples produced by bombarding silicon and germanium with a beam of gold ions

We demonstrate that surface ripples with an exceptionally high degree of order can develop when germanium is bombarded with a broad beam of gold ions. In contrast, if silicon is sputtered with an Au− beam, patches of ripples with two distinct wave vectors can emerge. These types of order can be understood if the coupling between the surface morphology and composition is taken into account.

Nanopatterning of mica surface under low energy ion beam sputtering

Irradiation of crystalline muscovite mica samples by 500 eV Ar+ ions at different incident angles can induce significant surface morphological variations. A periodic ripple pattern of nano-dimensions forms in the angle window 47°-70°. On the other hand, tilted conical protrusions develop on the surface at grazing incidence angles around 80°. From the derivative of the topographic images the distribution of the side-facet slopes in the ion incidence plane are measured, which is found to be strongly related to the pattern morphology. Additionally, it has been shown that, for the ripple structures, the base angles can be tuned by changing the ion fluence. An asymmetric sawtooth profile of the ripples obtained at low fluence is transformed to a symmetrical triangular profile at high fluence. As the slopes are found to be small, the pattern formation is not provoked by the gradient-dependent erosion mechanism rather it is the general effect of the curvature-dependent sputtering phenomena.

Formation and characterization of perpendicular mode Si ripples by glancing angle O2+ sputtering at room temperature

Off-normal low energy ion beam sputtering of solid surfaces often leads to morphological instabilities resulting in the spontaneous formation of ripple structures in nanometer length scales. In the case of Si surfaces at ambient temperature, ripple formation is found to take place normally at lower incident angles with the wave vector parallel to the ion beam direction. The absence of ripple pattern on Si surface at larger angles is due to the dominance of ion beam polishing effect. We have shown that a gentle chemical roughening of the starting surface morphology can initiate ripple pattern under grazing incidence ion beam sputtering (θ>64° with respect to the surface normal), where the ripple wave vector is perpendicular to the ion beam direction. The characteristics of the perpendicular mode ripples are studied as a function of pristine surface roughness (2–30 nm) and projectile fluence (5×1016–1.5×1018 O atoms cm−2). The quality of the morphological structure is assessed from the analysis of ion induc...

Mass and energy dependence of the sputtering yield of gallium arsenide

Abstract The sputtering yields of GaAs(100) bombarded at normal incidence by mass analyzed 40Ar+, 84Kr+ and 132Xe+ ions obtained from an electromagnetic isotope separator are determined in the energy range 15–35 keV. The experimental values of the sputtering yield obtained by the method of weighing the collected sputtered material are compared with the total sputtering yield calculated theoretically. The surface topography of a Xe+ bombarded sample is examined under SEM as an associated part of the multicomponent physical sputtering.

Photon emission in ion beam sputtering of an Mg target

Abstract Studies of excitation processes in sputtering due to bombardment of an Mg target with saturated oxygen coverage by 3–56 keV ions of various projectiles, namely, krypton, argon, neon, helium, oxygen and nitrogen have been carried out in a low energy ion beam facility developed in the laboratory. It is found that the relative excitation probability of the sputtered atomic and ionic species depends on the projectile mass as well as the energy. The results are discussed.